I had a very similar idea about a year ago. I was wondering if questions that started with Who, What, When, Where, How, Why, or Which were "general knowledge" questions, and might be automatically rejected. (This is a broader set than your suggestion.)
I did some quick experiment, which I documented here:
Can the quality of a question be judged by the first word in the title?
My conclusion was: As expected, they generally fared worse (on votes and rate of closure) than questions that started with Is, Are, Was, Were, Do, Does, Can, Has, Have or Did. However, the difference wasn't so stark that a blanket ban or other measure could be reasonably considered.
In short: I agree with the idea in principle, but the data only supported it weakly, not strongly.
(Notwithstanding that the effect might be much stronger if you limit it to only "Why" and "How".)